Piezo electric crystal



M mhs, 1932. EjQQHULBURT I 1,848,630

PIEzo ELECTRIC-CRYSTAL Original Filed Dec, 23, 1925 Edward 0. `llulburt.

Petenced Mer.`a,f1f932f UNITED STATES PATENT OFFICE Y EDWARD o.numwn'rfor wasnme'ron, ms'rnrc'r or comnmm f :erano-morale CRYSTALappneatieamea recenter as, -raars, serial No. 77,404. aenewea August s,rsa1.

My invention relates broadly to piezo-electric crystals moreparticular-lyto thev mounting of crystals and the provision of terminalsand loadedlilmsthe'reon for establishing connectionewith the surface ofthe crystals and determining the frequency o f operation thereof in"vacuum tube circuits.-

The object of my invention is to provide an arrangement of terminals forpiezo-electric crystals. V

Another object of my invention is to provide a conductive coatingforopposite faces of the piezo electric crystal in such a form and massthat the frequency of-oscillation of piezo-electric crystals maybe fixedwithin certain limits.

A further object of myvinve'ntion is to provide a coating of metal on a.crystal toy produce a. ,crystal unit havinga zero coetlicient offrequency change per degree change of temperature.

Oscillator systems utilizing. a crystal to control'the frequency providea means for holding the crystal between flat plates. Ex-

perience has indicated that films of oil, dust, etc. -destroy theoscillating pro erties of the` crystaland theexperience hasl edA totheinference that metallic filihsor adhering coatings would have' thesalnleinhibitplfyaction. I have -ei'ed,howeve,that me tallic filmswheudepositedby cathode sputter' bychemi'cal methods,or alike process, onot'havea deleterious A*effect on the crystal but on thevc'o'ntrary thecoatings seemto share to a gx-e'ater'or less extent t-hevvibra-l tionsof thecrystal-making it possible for the crystal so coated to be usedadvantageously as a. generator of sustained oscillations.

I have also discovered that the 4frequency of oscillation vof a coatedcrystal may be selectively 'fixed by varying the thickness of the filmsor by secu i to the films other materials by any suita soldering. v.

I have further discovered that by selectle process vsuch as ing suitablemetals to be used as the coating,- the temperature coeicient offrequency change ma be made tobe aero, an important factor in t eoperation of crystal'controlled circuits where the 'temperature of theapparatus may var from time to time which.,v

ordinarily in t e .casev of electrodes merely restin in contact with thesurfaces of the crysta would tend to cause a frequency shift. l Thepreferred location of the films is upon the opposite sides of thecrystal but I do not limit myself to such locatlons for the films macover the crystal entirely or only in part or y adding metal, such assolder, on a part of the coatings.

The single figure of drawing shows a crystal having coated surfacesaccording to my invention.

My invention has been illustrated in the attached diagram wherein theelectron tube V is shown with its electrodes connected in circuit withthe piezo electric crystal frequency determining system and with theoscillator circuit O.y The frequency determinin circuit includes thepiezo electric crysta Q having the films T deposited on opposite facesthereof in intimato contact ywith the crystal surface throughout thearea .vide af la er'of metal impregnated in the surfaceo the crystal.These films increase the elliciency ofv operation of the crystal asshown by the increased output of the circuits using crystals coated inthe manner herein disclosed. This increase in efficiency may be due toseveral causes, such as the elimination of brush discharge, leakage, `orperhaps thc concentration of the components of the stray oscillationswithin the crystal into oscillations along the desired axis.

Furthermore, the selection of the metal used, and the selection of thethickness of the metal film in relation to the dimensions of the crystalare important factors in the determination of the constants of theresultant crystal unit. By the variation in the constants of the metalfilm, a crystal may be controlled to operate the same or differentlyunder the varying conditions of operation, which varying conditions, forexample, may be a bread range of temperatures. Under the ordinaryconditions of operation it is most desirable to have a crystal that willinsure a constant frequency irrespective of the varying temperatureconditions under which it is operating.

With my system of coating crystals the wires that connect the crystalinto the circuits in which it may be used, may be secured to the filmsby solder or other like methods, thus assuring a lower Contactresistance than has heretofore been known.

Having thus described my invention what I claim as new is:

1. A. piezo electric crystal, metallic films deposited on the surfacesof said crystal, said films each adherin intimately to said crystal andhaving a thic ness proportioned to the natural frequency of the unloadedcrystal and the desired frequency of the loaded crystal for selectivelyfixing the frequency of operation of said crystal.

2. A piezo-electric crystal having a cathodical y deposited coating ofmetal upon each of its electrode surfaces, the thickness of at least oneof the coatings determined by the fundamental frequency of 'thepiezoelectric crystal and by the desired resonant frequency of thecoated crystal.

3. A piezo-electric crystal having a cathodically deposited coating ofmetal upon each of its electrode surfaces, the thickness of each of thecoatings determined by the fundamental frequency of the piezo-electriccrystal and by the desired resonant frequency of the coated crystal.

4. The method of adjusting the free vibration period of a piezo electricelement which comprises grinding said element to a thickness slightlyless than that corresponding to the free vibration period desired forsaid element, and applying a conductive coating to a lateral surface ofsaid element for changing its free vibration period to the desiredvalue.

5. The method of adjusting the free vibration period of a piezo electricelement which comprises grinding said element to a thickness slightlyless than that corresponding to the free vibration period desired forsaid element, applying a metallic coating to a lateral surface of saidelement, and adjusting the average thickness of said coating and elementto a value corres onding to the deaired free vibration eriod EDW `RD O.HULBURT.

